[TXnMA]

I thought relativity said that there is no preferred inertial reference frame.

By arranging to act simultaneously, they placed themselves in the same reference frame.

BTW, could that IRF be described as "approximately SunTime + [(1/c) X 1AU]" ? '-)

Regards!

[TXnMA]

Hmmm -- I note that I referred to position [of the earth's center] (an average radius of 1AU from the sun) -- which impies an position on a sphere of radius = 1AU, centered on the Sun.

To be more accurate, I suppose that position would have to be defined including the date to derive relative motion between earth and sun, since the earth's orbit is not circular...

But, you are correct -- inasmuch as I had to refer to position (relative to the Sun, whch has its own [constantly changing WRT the Galaxy center, etc.] position)...

Of course, by convention, "earth time" is measured at the Prime (Greenwich) Meridian. Your watches merely indicate your angular displacement (± 7.5 degrees) from the Prime meridian. Again, as you point out -- position...